Influence of the chemical synthesis on the physicochemical properties of N-TiO2 nanoparticles

Nitrogen doped TiO2 materials were successfully prepared following three different preparation routes (sol–gel, hydrothermal and pyrolysis) and characterized by various spectroscopic techniques. All samples absorbed radiation in the visible range and were active in the photocatalytic degradation of cyanotoxin microcystin-LR under visible light and in acidic conditions. The different preparation routes led to the formation of various impurities into the solids. In the case of hydrothermal and sol–gel samples, these impurities were weakly bound at the surface whereas the materials prepared by pyrolysis, the impurities showed a relevant stability and could not be removed even at high temperature. These species can affect the photocatalytic performance in different ways depending on their bulk or surface nature. On the basis of the photocatalytic data illustrated in this paper, the presence of such species at the surface was not detrimental for the photocatalytic activity of nitrogen doped TiO2 but actually contributed to a higher interaction with the target cyanotoxin; leading to a higher photocatalytic activity than that observed for samples prepared via the classic sol–gel method.